Commonly owned U.S. Pat. Nos. 5,341,870 issued Aug. 30, 1994 and 5,533,259 issued Jul. 9, 1996, both to Hughes et al, the complete disclosures of both of which are herein incorporated by reference, disclose unique evaporators for refrigerants that are ideally suited for use in residential air-conditioning applications. While the structures disclosed in the Hughes et al patents work well for their intended purpose, and indeed are a considerable improvement over conventional evaporators employed in air-conditioning systems, they are subject to the same difficulties in terms of efficiency if the refrigerant is not properly distributed within the evaporator.
When poor distribution occurs, one section of the evaporator core is often flooded with liquid refrigerant while another section is essentially starved of refrigerant. An example of poor distribution, based on the infrared thermal image of an actual evaporator, is shown in FIG. 1. This distributor is of the general configuration illustrated in the above identified Hughes et al patents and is of the type wherein one header 10 may be provided with an inlet fixture 12 and the opposite header 14 provided with an outlet fixture 16. That is to say, the evaporator illustrated is what is known in the trade as an end feed, end draw, "V" evaporator of the parallel flow variety.
The tubes interconnecting to headers 10 and 14 are schematically illustrated at 18 and of course, serpentine fins (not shown) extend between adjacent ones of the tubes 18.
In such an evaporator, tubes which are starved of refrigerant quickly run out of liquid or mixed refrigerant. Consequently, sizable percentages of the length of each starved tube contain only single phase, superheated gaseous refrigerant. Heat transfer is poor.
Furthermore, air side surface temperatures where there is superheated gas flow are typically above the dew point and consequently, there will be no condensation of moisture from air flowing through the evaporator in those areas of superheated flow. Thus, no dehumidification takes place in those areas.
Where dehumidification does take place, moisture will be present on the exterior of the tubes and will increase the resistance to airflow through the evaporator at those locations. That is to say, airflow resistance will be less in those areas of superheated flow and consequently, the superheated areas receive a disproportionate amount of the total airflow through the evaporator, further reducing efficiency.
Flooded tubes produce excellent heat transfer throughout but often fail to evaporate all of the liquid refrigerant. Consequently, the unevaporated refrigerant is not put to use and the work employed in condensing the vapor to a liquid is essentially wasted. Furthermore, the presence of unevaporated liquid in the suction line may cause thermal expansion valves used in the system to "hunt." Unstable operation will result.
As seen in FIG. 1, areas wherein superheated gas flow occurs are shaded. In contrast, the nonshaded areas indicate proper functioning areas or areas where the tubes are flooded.
The present invention is directed to achieving a more uniform distribution of refrigerant in evaporators generally and in "V" evaporators of the parallel flow variety by eliminating or minimizing areas in the evaporator core that may be starved of refrigerant and result in excessive superheating of refrigerant.